docs: add registry (quay.io/) for pre-loading images for kind

in doc, it recommends docker pull image, but the command is :
  docker pull cilium/cilium:|IMAGE_TAG|

this will download from docker.io
However, in operator, it loads images from quay.io
we should keep them the same, otherwise, we download for nothing.

Signed-off-by: adamzhoul <adamzhoul186@gmail.com>

Documentation/gettingstarted/kind-preload.rst

@@ -2,5 +2,5 @@ Preload the ``cilium`` image into each worker node in the kind cluster:
 
 .. parsed-literal::
 
-  docker pull cilium/cilium:|IMAGE_TAG|
-  kind load docker-image cilium/cilium:|IMAGE_TAG|
+  docker pull quay.io/cilium/cilium:|IMAGE_TAG|
+  kind load docker-image quay.io/cilium/cilium:|IMAGE_TAG|